Method of spatulating packaged dental filling

ABSTRACT

Pre-packaged dental filling ingredients for use by dentists. The ingredients which are in part liquid and in part powder are encapsulated and sealed tightly in a flexible-membrane formed bag and therein separated one from the other which separation is released by the compression of the bag to cause the ingredients to be successively brought into contact and mixed together. The mixture, confined within the bag, is spatulated to form a paste or semi-solid, ready for application to a patient&#39;&#39;s tooth. The spatulation may be carried out advantageously with apparatus adapted to compressively roll over the flexible bag supported on a surface or squeeze the bag against the surface.

United States Patent 1 lnoue et al.

[ 1 Mar. 27, 1973 METHOD OF SPATULATING PACKAGED DENTAL FILLINGInventors: Kiyoshi lnoue, Tokyo; Akihiko Shimizu, Sagamihara, both ofJapan Assignee: lnoue Japax Research Incorporated,

Yokohama-shi, Kanagawa, Japan Filed: Nov. 12, 1970 Appl. No.: 88,738

Foreign Application Priority Data Nov. 15, 1969 Japan ..44/92248 Nov.15, 1969 Japan ..44/92249 US. Cl. ..259/72, 206/47 A, 206/635, 259/D1G.20, 259/DIG. 46 Int. Cl. ..B01f 13/08 Field of Search.....206/47 A,63.5; 259/DlG. 20, 259/72, 1 R, DIG. 46

References Cited UNITED STATES PATENTS 12/1966 Schneider et al. ..206/47A 2,971,851 2/1961 Kurtz ..206/47 A X 1,509,161 9/1924 Mauter... ..32/l53,332,670 7/1967 Swartz ....259/72 X 3,595,439 7/l97l Newby.......206/47 A 3,572,997 3/1971 Burk ....206/47 A 3,608,709 9/1971 Pike..206/47 A Primary ExaminerRobert W. Jenkins Assistant Examiner-PhilipR. Coe Attorney-Owen, Wickersham & Erickson [57] ABSTRACT Pre-packageddental filling ingredients for use by dentists. The ingredients whichare in part liquid and in part powder are encapsulated and sealedtightly in a flexible-membrane formed bag and therein separated one fromthe other which separation is released by the compression of the bag tocause the ingredients to be successively brought into contact and mixedtogether.

The mixture, confined within the bag, is spatulated to form a paste orsemi-solid, ready for application to a patients tooth. The spatulationmay be carried out advanta'geously with apparatus adapted tocompressively roll over the flexible bag supported on a surface orsqueeze the bag against the surface.

2 Claims, 17 Drawing Figures Patented March 27, 1973 3,722,833

3 Sheets-Sheet 1 INVENTORS KIYOSHI INOUE AKIHIKO SHIMIZU I29 BY ATTORNEYS Patented March 27, 1973 3,722,833

3 Sheets-Sheet 2 INVENTORS KIYOSHI INOUE AKIHIKO SHIMIZU ATTORNEYSMETHOD OF SPATULATING PACKAGED DENTAL FILLING BACKGROUND OF THEINVENTION The invention is in the field of dentistry and especiallyrelates to a method of preparing a dental filling in paste or semi-solidform based on the new concept.

When a dentist prepares a dental filling from a plurality ofingredients, it has hitherto been a common requirement that heaccurately measure out such ingredients from vials or the likecontaining individual ingredients and mix them together with instrumentsor utensils. This has been necessary because of the fact that they mustbe mixed together immediately before use. One of such ingredients iscommonly a liquid or a number of different liquids and the other is apowder or a number of powders or different materials which are reactableor complementary to such liquid appropriate to the kind and type of adesired filling, and a suitable procedure must be made during the mixingstage to accomplish reactions uniformly over the entire region of thepowder and liquid in a relatively short time. For example, when such afilling as zinc-phosphate, silicate or silico-phosphate cement is to beprepared, the liquid is an aqueous solution containing phosphoric acid,and the powder is made up from one or more of zinc oxide, silicon oxideand aluminum oxide, along with one or more additives, the exactcomposition depending on the particular cement desired, and the powderand liquid are mixed together and spatulated fully until the mixturebecomes a paste which can be applied to a patients tooth or teeth. Inphenomenon, when the powder and liquid are brought into contact,exothermic reactions are brought about to form phosphate, acid phosphateand other products in crystal and noncrystal forms, with the localcrystalization being apparently followed by the solation and gelation ofthe mixture while the paste commences and proceeds setting or curingwith a final structure in which unreacted cores of powder aredistributed among the reaction formed crystals.

Quantities of starting materials to be measured out and control of thesecomplex reactions which are to be accomplished in a relatively shorttime are critical inasmuch as these are factors largely governing thefinal structure of the fully set product which determines the qualitythereof as a dental filling. However, heretofore, these factors havebeen left to dentists who will attend to mixing or spatulation procedurein various conditions and at various levels of skill for such procedure.Moreover, it has been common, especially where spatulation procedure andthe like is essential, that such is carried out with the mixture exposedto the environmental atmosphere whose conditions vary from season toseason and from place to place. As a consequence, the strength and otherquality characteristics of the resulting filling have largely varieddepending on the humidity and the temperature of the particularenvironment in which it is prepared. The quality values have been ofteninferior to required standard values and this tendency is rather commonin the humid and hot seasons.

SUMMARY OF THE INVENTION It is the primary object of the presentinvention, therefore, to provide an improved technique which makes itpossible to prepare from a plurality of starting materials a dentalfilling of a superior quality, i.e. compressive strength, hardness,freedom of dimensional change (expansion or shrinkage), adhesiveness andinterlockability, practically independently from the environmentalconditions in which the filling is prepared.

Another object of the present invention is to provide a method ofpreparing a dental filling which relieves the dentists of the tediousbother of actually measuring out starting materials or ingredients asheretofore required and enables fabrication of a dental filling ofsuperior characteristics to those heretofore obtained in standardconditions.

These objects and others which will become apparent hereinafter, areattained in accordance with the present invention, by our novel conceptof packaging in mutual separation until just before use a plurality ofpremeasured substances adapted to form a dental filling, i.e. pastecement or amalgam, and releasing the separation to cause said separatedsubstances to be successively brought into contact and mixed togetherand effecting reaction therebetween controlledly and uniformly within aconfined space isolated from the atmosphere under compressive or squeezeaction applied to the mixturejln accordance with an important aspect ofthe invention, there is provided a capsule comprising aflexible-membrane formed bag enclosing premeasured amounts of thesubstances which are tightly separated from one another in the bag, saidseparation being releasable by the compression of the bag to cause thesubstances to be successively mixed together within the bag, the latterbeing of thickness and material adapted to withstand saidcompression andfor rupture or breakage only by the users purpose to take out themixture or product for clinical use.

The invention is applicable to any of the dental fillings available andthe plural substances for packaging in a bag are those choosenrespectively depending on the particular end product desired. Forexample, for a zinc-phosphate cement, the first substance is a powercontaining zinc oxide and for a silicate cement, the powder containsmainly admixed silica and alumina. As is well known, various additivesmay be admixed to these oxides to facilitate and/or control exothermicreactions brought about as the primary constituent and a liquid aremixed together. Common to these particular cements, liquid isconstituted by or contains an aqueous phosphoric acid solution. Also fora water settable phosphate cement, the powder may be of phosphate saltand/or acid phosphate salt and the liquid a suitable solvent such aswater or alcohol. For amalgam, the liquid is mercury and the powdercopper or copper alloy.

The bag may be a thin rubber, plastic, natural or synthetic resin andrequisites of the material forming same are flexibility and toughness towithstand the compressive force applied thereto as well asnondestructability by liquid and exothermic reactions. Among others, apolyester has been found highly suitable for this purpose.

For the purpose of the present invention, the

end, a pack may be prepared of a diaphragm filled with a liquid forenclosure as a first compartment within the flexible bag with the spacebetween the outer surface of this diaphragm and the inner surface of thebag filled with powder forming the second compartment. In this can beprepared by bonding portions of the bag so as to sealingly separate theliquid or liquids from the powder or powders, this bond beingsufficiently tight to prevent release of the separation in the absenceof such compressive force are applied to the bag for mixing purpose.

According to a preferred embodiment of the invention, a plurality ofpackages set forth above may be prepared which are disconnectably linkedin series to permit the dentist to separate one from the series at hisneed.

The method of preparing a dental filling in a paste or semisolid formmaking use of a sealed package with separated ingredients or startingsubstances, according to the present invention, includes applying acompressive, squeezing force to the flexible package supported on asuitable surface in the atmosphere or preferably within a coolant ortemperature-controlled fluid so as to cause the separated substances tobe successively brought into contact and spatulated sustaining reactionsbetween them within the confined space of the package. While any knowninstrument may be used to spatulate the mixture left in the closedspace, we prefer to this end the use of a rotary member adapted tounidirectionally reciprocatingly roll over the package against asupporting surface under compression or relatively convex members orsurfaces adapted to squeeze the package between them.

DESCRIPTION OF THE DRAWINGS FIG. 1A is a sectional view of a capsuleembodying the principles of the present invention;

FIG. 1B is a cross-sectional view of the embodiment on the line 13-13ofFIG. 1A;

FIG. 2 is a sectional view of another form of the capsule according tothe invention;

FIG. 3 is a plan view of another embodiment of the capsule according tothe invention;

FIG. 4A is a plan view of a capsule of the invention embodied in anotherform;

FIG. 4B is a cross sectional view of the capsule taken on the line 4B-4Bof FIG. 4A;

FIG. 4C is a cross sectional view of a similar capsule;

FIG. 5 is a diagrammatic view of apparatus for performing thespatulation procedure according to the present invention;

FIG. 6 is a diagrammatic enlarged view illustrating a spatulatingprocedure according to the invention;

FIG. 7 is a diagrammatic top view of another form of a hand-operatedspatulator according to the invention;

FIG. 7A is a side elevational view of the apparatus of FIG. 7;

FIG. 8 is a sectional view in a diagrammatic form of a motor-operatedspatulator according to the present invention;

FIG. 8A is a top view in cross section of the spatulator of FIG. 8;

FIG. 9 is a diagrammatic representation of another form of spatulatingapparatus according to the invention;

FIG. 10 is a side-elevational view of still another form of amotor-operated spatulator and FIG. 10A is a front view, partlyfragmentary, thereof; and

FIG. 11 shows rotary members of various configuration'useful inperforming the spatulation procedure according to the present invention.

DETAILED DESCRIPTION In FIGS. 1A and 18 there is shown one illustrativeembodiment of our novel dental capsule packaging a liquid and a powderin tight mutual separation. The capsule l is in the form of a closed bagmade from a flexible membrane 2 whose interior is divided into multiplecompartments filled with individual ingredients or starting substances,here, into two compartments 3 and 4 filled with a liquid and a powder,respectively, and separated by a flexible diaphragm 5. In this example,the latter diaphragm is of a material, thickness and character adaptedto tightly separate liquid and powder normally but for rupture torelease the separation when compressive, squeezing action is applied tothe bag I as will be described. The membrane 2 forming the bag 1 issufficiently flexible, tough and thick to withstand such compressive,squeezing action so as to confine the mixture within the space isolatedfrom the environment. This capsule may be a pair of tubes closed at bothends with the first tube 5 filled with a premeasured amount of liquidand the second tube 2 containing a premeasured amount of powder in thespace between its inner wall and the outer wall of the liquid-filledclosed tube to form a sausage-shaped container with two compartmentsfilled with liquid and powder respectively. For the users convenience, aplurality of such capsules may be prepared which are linked in series.Thus, the user can cut the portion c to separate the terminal capsulefrom the series for his intended use and spatulation procedure. Thecapsule of FIG. 2 is shown to include a liquid compartment 3 subdividedinto plural compartments each filled with a amount of liquidcomplementary to those filled with the other subcompartments relative toan amount of powder contained in the bag 2 in contact therewith and thesubcompartments. Each of the latter is adapted for rupture ascompressive, squeezing action is exerted, as will be described.

In each single capsule which may be one of various' forms as shownbefore and hereafter, it is of course necessary to package specifickinds of powder and liquid in accurately measured amounts and proportiondepending on the type and amount of a particular dental filling. As setforth earlier, phosphate cements make use of a powder containing oxidesand a liquid containing an phosphoric acid solution, or otherwise apowder containing phosphate salt and a solvent liquid. The powder mayinclude one or more additives to improve the quality of a final productasformed. While innumerable additives have been suggested by others, oneof the joint inventors of the present invention,

Kiyoshi lnoue, has discovered that inclusion up to 5 percent by volumeof finely divided fibers (of 0.1 to 3 micron diameter and 0.5 to mmlength) of a synthetic resin not detrimental to the tooth body (such aspolypropylene, trifluoride resin, vinyl chloride, chlorinated polyester,polyethylene, furan, epoxy resin, polyester, phenol resin and the like)greatly improves the compressive strength and the interlocking strengthof any of these cements as applied to a tooth.

Shown in FIG. 3 is another embodiment of our novel capsule which is inthe form of a rectangular, relatively flat envelope in which twocompartments 3 and 4 sealed tightly from the environment are here againfilled with a premeasured quantity of liquid and a premeasured quantityof powder respectively and interdivided by a boundary 5 for isolatingthe accurately measured liquid and powder from one another until justbefore a dental filling as the product therefrom is desired for use.This boundary is for the indicated function as well as the function torelease the isolation to cause these sealed contents to be mixedtogether. To this end, the capsule may be prepared by overlapping twoflexible, plastic (e.g. polypropylene) sheets for a thickness, say, 0.05mm and bonding the overlapped sheets permanently except those portionsfor forming compartments 3 and 4 and boundary 5, the latter being formedby tightly but fluid-pressure releasably bonding the correspondingoverlapped portions of the sheets. In this case, the specific manner ofbonding the sheets and filling liquid and powder may be that bothelongated sides A and A of the overlapped sheets are permanently bondedand the sheets then semi-bonded along 5' or vice versa. Thencepremeasured amounts of powder and liquid (e.g. 1.0 g powder and 0.36 ccliquid, for example, in the case of zinc phosphate cement) are enteredinto regions 4 and 3 (each with three sides closed) from open ends B andB, respectively and finally the regions B and B are permanently bondedto a two-compartment envelope as shown. The semi-bond at 5 is made at anadequate tightness so as not to lose the bond under normal conditionsbut to do so when a squeezing action is applied to the envelope fromregion 3 to region 4 at a reasonable compressive force. To make suchsemi-bond and permanent-bond selectively, a conventional heat sealer isfound highly suitable. In the mass production of a number of identicalpackages as shown, identical bonding or sealing conditions may befollowed. To the completed envelope or package, designation of a fillingto be made, liquid and powder contents and a specific manner ofspatulation procedure may also be printed for the users convenience.

In FIGS. 4A and 48, there is shown another form of capsule which is hereagain a rectangular envelope formed from two plastic sheets permanentlybonded along the margin and having releasably separated two compartments3 and 4 filled with a liquid and a powder, respectively. Theliquid-filled compartment 3 may be a tube of a rupturable diaphragmwithin the outer bag or envelope (FIG. 4B) and in contact with thepowder filled compartment 4 as in FIG. 1A, or otherwise may be ofmembrane integral with the envelope and semibonded along boundaries 5"as in FIG. 4C to separate the liquid from the powder.

Thus, packages for the various types and amounts of various dentalfillings can be prepared and distributed to dentists who may merelychoose one package adapted for a particular clinical purpose without theneed of actually attending to, as heretofore, the work of measuring outstarting materials with high accuracy because of high criticality ofsuch accuracy largely influencing the quality of the end product. Thepackage, therefore, eliminates completely not only the dentistsconventional need for such tedious preparatory work but also thedeterioration of product fillings due to rough measuring of startingmaterials or entry of impurity as have been often the case heretofore.

In FIG. 5 there is shown in a diagrammatic view a spatulator 10 forforming a dental filling when used with a package illustrated in theforegoing figures. The spatulator includes a base 11 provided with aplanar surface for supporting a package 1 securely in contact thereonwith a pair of clamps 12a and 12b. It also is provided with a lever 13whose one end 14 is hinged at a stand 15 secured to base 11 and its freeend 16 is adapted for the users grip for the spatulation operation.Lever 13 has a cross arm 17 hinged at 18 which serves as a shanksupporting a rotary member 19 adapted for free rotation about its axis20 and the shank is also spring-held with lever 13 as indicated. Therotary member 19 is thus adapted to reciprocatingly roll over thepackage 1 squeezing the latter against the supporting surface 11 aslever 16 is reciprocatingly swung. The initial compression of thepackage will rupture diaphragm 5 (FIGS. 1A, 1B, 2 and 4B) or releasesemi-bond 5', 5" (FIGS. 3 and 4C) to bring the liquid and powdertogether within the capsule, with the subsequent squeezing with theroller 19 causing the liquid and powder to be homogeneously mixedtogether effecting reaction as the compressed zone continuously shiftsbetween the two surfaces 19 and 11, one flat and one convex or round, asshown in FIG. 6. Therefore, unlike the conventional practice, not onlyis the spatulation advantageously carried out isolated from the humidityof the surrounding atmosphere, but also the heat generated by exothermicreactions is effectively scattered or dissipated by relatively largesurfaces which rollingly squeeze the encapsulated mixture between them,with the quality of the resulting product filling bearing practically nodependency on the environmental conditions. Moreover, the spatulationwith such an encapsulated mixture permits no entry of any impurity whichwould be detrimental to the quality of the product filling and does notsoil the area used therefor.

Furthermore, the spatulation operation is much simplified and the usermay simply repeat such a reciprocating squeeze by a given number, say 50to 200 times, with substantially a constant time of each reciprocationalthough such parameters and the entire period for the spatulation arechoosen depending on the kind and characteristics of a particularfilling desired. Indeed, it has been found that in this manner, fillingsof any particular type are prepared practically without variation inquality and of the quality much superior to those having beenattainablewith standard techniques.

With usual dental fillings as prepared through chemical and curingreactions, the environmental temperature is sometimes or otherwise oftencritical to the quality of the filling prepared and applied for a givenuse where the temperature greatly influence the rates of reactionsinvolved in the paste forming stage. While with the present invention,the heat generated by the exothermic reactions is effectively scatteredand thus such reactions are advantageously held to proceed at moderaterates while the individual starting materials are brought into contactand spatulated together, it is sometimes desirable to control'theenvironmental temperature especially where the latter differs much froman optimum or standard temperature at which particular filling materialsare made into pastes. For such situations, a temperature control may bemade here by maintaining the temperature of plate 11 at a desired value(e.g. circulating a temperature of plate 11 at a desired value (e.g.circulating a temperature-control fluid therethrough of contacting atemperature control electronic element thereto) or preferably immersingin a temperature-control fluid the region of capsule 1 subjected tocompressive squeezing action.

In FIG. 7, there is shown another form of handoperated spatulatoraccording to the present invention. This embodiment includes a rotarymember 119 which is rotatably supported by a grip 116 via a shaft 125which is journaled either on roller 119 or grip 116 and secured with theother. On a spatulating plate 111, there is secured a package 1 such asis shown in FIG. 3 with a pair of spring clamps 112a and l12b stretchingthe package between them and the user may hold the package in a positionand in contact with a supporting surface 111 with two fingers of hisleft hand. The operator may hold grip 116 with his right hand, bringrotary member 119 upon the package 1 and squeeze the package againstsurface 111. The peripheral surface of the rotary member is here madesufficiently frictional relative to the surface of package 1 and formingthis member of a rubber and providing cracks thereon as shown are foundhighly advantageous to promote the squeezing action.

The spatulation process according to the present invention may also becarried out, when the economy permits, while passing an electric currentof microampere order through the mixture subjected to compressive andsqueezing action. To this end, as shown in FIG.

7A an electromagnet 127 is provided behind spatula-- tion plate 111 aswound by a coil 128 connectable with an alternating-current or pulsesources 129 via switch 130. It will be seen that the closure of switch130 causes electromagnet 127 to create an oscillatory magnetic'fieldwhich by electromagnetic induction creates an eddy current through themixture spatulated within capsule 1. This electric treatment is found toyield to percent increase in hardness of resulting cements.

In FIGS. 8 and 8A, we show a motor-operated spatulator using a pair ofrotary members 1 and 2 for compressively squeezing a capsule betweenthem as they are relatively displaced. In this spatulator, the capsuleis clamped on the periphery of first rotary member 1 along lb-lc asshown FIG. 8A, adapted in contact with the periphery of second rotarymember 2 whose shaft 2a is rotatably secured to an arm 3 which at itsone end 3a is hingedly as secured to a cover table 9. The other end 3bof this arm is biased by a tension spring 4a connected with a biasingmeans so as to urge rotary surface 2 against first rotary member 1 at asuitable pressure adjusted by biasing means 4.

The drive means for these rotary members comprises a motor 5 mounted onbase 8 and whose output shaft is connected by a reduction transmission 6with the shaft 1a journaled through bearing 9b, to rotate the firstrotary member 1 in one direction and to inductively rotate second rotarymember 2 in the opposite direction by the friction between thecontacting surfaces. Such rotary motion is preferably reciprocal r0,-tary motion and, to this end, a rotation reciprocator 7 is provided formotor 5 and can be such that a predetermined angie of rotation in onedirection of motor 5 operates a limit switch to reverse the direction ofrotation of the motor.

In order to enable the operation in a temperature controlled conditionwhich, as set forth earlier, is desirable when the environmentaltemperature differs considerably from an optimum or standard temperatureat which the spatulation is to be made, the apparatus may be equippedwith a suitable temperature control means. To this end, a housing 10 ishere mounted on cover table 9 for reception of a coolant or temperaturecontrol liquid as supplied through a conduit 11 and a valve 12 and asuitable gasket 9a is provided to prevent leakage of the liquid whichimmerses rotary members 1 and 2 and the region of spatulation.

In operation, after a capsule is clamped on the specific location of theperiphery of first rotary member 1, bias means 4 is adjusted to urgesecond rotary member 2 against the first at a pressure which would besufficient to release the separation of the divided contents within thecapsule when the latter is brought into the interface of theserelatively urged members. Container 10 is mounted on cover 9 with gasket9a and a fluid is fed into the container from pipe 11 by opening valve12 until rollers 1 and 2 are sufficiently immersed within the liquid.Then, motor 5 is switched into drive and rotary member 1 carrying thepackage is reciprocatingly turned by an angle while rotary member 2 isinductively turned by the corresponding angle to reciprocatingly squeezethe capsule progressively compressed between them. The pressure increaseof the liquid compartment during the initial turn will release theseparation between the liquid and powder which are then homogeneouslyspatulated in situ within the confined space of the capsule by holdingmotor 5 in operation for a given time period. Therefore, the quality ofthe resulting product filling is totally independent of the users skill.

In the embodiment shown in FIG. 9, a capsule is again held on a rotarymember 1 but a pair of other rotary members 2 and 2' each with adiameter greater than that of rotary member 1 are used to squeeze thecapsule as the latter carried on first rotary member is urged againstthe other two rotary members alternately. Rotary member 2 is rotated inone direction by a motor 18 through a pulley 14a continuously and rotarymember 2' is rotated in the opposite direction by a pulley connectingsame with rotary member 2. A cam 13 is provided driven by a motor 18synchronously with rotary members 2 and 2'. First rotary member 1 isrotatably held by a support member 1b which extends through a leafspring 16 to an arm 15, these members being hinged at 15a and the oneend of arm 15 being in contact with cam surface 13 as urged by expansionspring 17.

ln H68. and 100, we show another form of method and apparatus forperforming the spatulation of an encapsulated filling material inaccordance with the present invention. In this embodiment, a capsule isheld on a planar surface 2 as in some of previous FIGURES and squeezedthereagainst by a rotary member 1. The rotary member 1 has a shaft larotatably journaled and resiliently held by spring 4 in an aperture 3aformed in an upright extending arm 3. The lower end 3c of this uprightarm is pivotally secured to the lateral face of machine base 8 andhinged to make the arm 3 swingable in a plane perpendicular tospatulation surface 2a. Intermediary of the upper end portion 3a and thelower end 3c, the arm is formed with an elongated aperture 3b of alength substantially equal to the diameter of a disk 5 as will bedescribed. The disk 5 is rotated via a reduction transmission 7 by amotor 6 mounted on the base 8 and has on one of its face a protrusion 5aas shown which is adapted to be slidably engaged in aperture 3b so thatthe rotation of motor 6 causes protrusion 5a to travel along a circlewhile being slidably held in aperture 3b of the arm 3 which thusreciprocatingly swings over an angle about hinge 3c to cause rotarymember 1 to reciprocatingly roll over surface 2a by friction compressingthe package thereagainst under a pressure effected by spring 4.

In FIG. 11, there are shown rotary members of various forms which may beused with the foregoing apparatus. Each of these rotary members may bemade from a plastic and preferable from a material having a high thermalconductivity such as aluminum to dissipate the heat generated byreactions to the extent that such reactions are carried on at acontrolled rate. Also, if desired, a cooling element may be embedded inthe rotary member.

We claim:

1. A method of preparing a dental filling in paste form from a pluralityof starting materials including a liquid and a powder, comprising thesteps of:

encapsulating within a flexible-membrane-formed bag premeasuredquantities of said liquid and said powder with one separated from theother therein, providing a compressive motion onto said bag by squeezingit between a flat surface and a convex surface at a pressure and ofcharacter sufficient to release said separation, thereby causing saidliquid and powder to be successively brought into contact and mixedtogether to form a paste within the confined space of said bag, the zoneof compression shifting progressively over the bag to cause the paste tobe spatulated within said bag, and applying an oscillatory magneticfield to said bag and the mixture therein as said bag is being squeezed,said magnetic field inducing an electric current of microampere order topass through said mixture.

2. A method of preparing a dental filling in paste form from a pluralityof starting materials including a liquid and a powder, comprising thestep of:

encapsulating within a flexible-membrane-formed bag premeasuredquantities of said liquid and said powder, providing a separationbarrier between them,

exerting a squeezing force on the bag to rupture the separation barrierand to mix the liquid and powder together to form a paste within theconfined space of the bag, while shifting the force progressively overthe bag to cause the paste to be spatulated within said bag, andapplying an oscillatory magnetic field to said bag and the mixturetherein while said squeezing force is being exerted, said magnetic fieldinducing an electric current of microampere order to pass through saidmixture.

1. A method of preparing a dental filling in paste form from a pluralityof starting materials including a liquid and a powder, comprising thesteps of: encapsulating within a flexible-membrane-formed bagpremeasured quantities of said liquid and said powder with one separatedfrom the other therein, providing a compressive motion onto said bag bysqueezing it between a flat surface and a convex surface at a pressureand of character sufficient to release said separation, thereby causingsaid liquid and powder to be successively brought into contact and mixedtogether to form a paste within the confined space of said bag, the zoneof compression shifting progressively over the bag to cause the paste tobe spatulated within said bag, and applying an oscillatory magneticfield to said bag and the mixture therein as said bag is being squeezed,said magnetic field inducing an electric current of microampere order topass through said mixture.
 2. A method of preparing a dental filling inpaste form from a plurality of starting materials including a liquid anda powder, comprising the step of: encapsulating within aflexible-membrane-formed bag premeasured quantities of said liquid andsaid powder, providing a separation barrier between them, exerting asqueezing force on the bag to rupture the separation barrier and to mixthe liquid and powder together to form a paste within the confined spaceof the bag, while shifting the force progressively over the bag to causethe paste to be spatulated within said bag, and applying an oscillatorymagnetic field to said bag and the mixture therein while said squeezingforce is being exerted, said magnetic field inducing an electric currentof microampere order to pass through said mixture.